Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 28, 2017	Jan. 23, 2016	Jan. 28, 2017	Jan. 23, 2016
Net periodic pension costs
Service cost	$ 320	$ 333	$ 958	$ 999
Interest cost	1,170	1,211	3,510	3,633
Expected return on plan assets	(1,245)	(1,226)	(3,735)	(3,678)
Net amortization	764	736	2,292	2,208
Net periodic pension cost	$ 1,009	$ 1,054	$ 3,025	$ 3,162